Add strong types for JSON.stringify

Author: sstur

src/entrypoints/json-stringify.d.ts

@@ -0,0 +1,24 @@
+interface JSON {
+  /**
+   * Converts a JavaScript value to a JavaScript Object Notation (JSON) string.
+   * @param value A JavaScript value, usually an object or array, to be converted.
+   * @param replacer A function that transforms the results.
+   * @param space Adds indentation, white space, and line break characters to the return-value JSON text to make it easier to read.
+   */
+  stringify<T = any>(
+    value: T,
+    replacer?: (this: any, key: string, value: any) => any,
+    space?: string | number
+  ): undefined extends T ? string | undefined : string;
+  /**
+   * Converts a JavaScript value to a JavaScript Object Notation (JSON) string.
+   * @param value A JavaScript value, usually an object or array, to be converted.
+   * @param replacer An array of strings and numbers that acts as an approved list for selecting the object properties that will be stringified.
+   * @param space Adds indentation, white space, and line break characters to the return-value JSON text to make it easier to read.
+   */
+  stringify<T = any>(
+    value: T,
+    replacer?: (number | string)[] | null,
+    space?: string | number
+  ): undefined extends T ? string | undefined : string;
+}

src/tests/json-stringify.ts

@@ -0,0 +1,27 @@
+import { doNotExecute, Equal, Expect } from "./utils";
+
+doNotExecute(() => {
+  const result = JSON.stringify(undefined);
+  type tests = [Expect<Equal<typeof result, string | undefined>>];
+});
+
+doNotExecute(() => {
+  const result = JSON.stringify(5 as undefined | number);
+  type tests = [Expect<Equal<typeof result, string | undefined>>];
+});
+
+doNotExecute(() => {
+  const result = JSON.stringify(undefined as any);
+  type tests = [Expect<Equal<typeof result, string | undefined>>];
+});
+
+doNotExecute(() => {
+  const result = JSON.stringify(undefined as unknown);
+  type tests = [Expect<Equal<typeof result, string | undefined>>];
+});
+
+doNotExecute(() => {
+  const value: null | string | number | boolean | object | Array<any> = null;
+  const result = JSON.stringify(value);
+  type tests = [Expect<Equal<typeof result, string>>];
+});